1. Field of the Invention
The present invention relates to a highly integrated semiconductor memory device and a method for fabricating the same, and more particularly to a semiconductor memory device capable of reducing a memory cell area and yet having a sufficient charge storage capacity.
2. Description of the Prior Art
As semiconductor memory devices such as general direct random access memory have a higher integration degree, they involve a problem of having an insufficient charge storage capacity. This is because the higher integration degree results in a great decrease in occupied area of memory cells and thereby a decrease in surface area of storage electrodes. In a conventional case shown in FIG. 1, actually, a storage electrode 11 constituting a memory cell together with a field effect transistor has a surface area sharply reduced in proportion to a decrease in occupied area of the memory cell because it is formed over the field effect transistor to have a plane plate shape. Furthermore, the plane plate shape of the storage electrode results in a difficulty to increase the surface area of storage electrode.
As shown in FIG. 1, the conventional semiconductor memory device includes a field oxide film 2 formed on the semiconductor substrate 1, a gate insulating film 3 and a word line 4 both formed at an element region of the semiconductor substrate 1, oxide film spacers 5 respectively formed on side walls of the word line 4, and source and drain regions 6 and 6' formed at a portion of semiconductor substrate 1 exposed by an impurity ion injection process. Over the entire exposed surface of the resulting structure, a planarizing insulating film 7 is coated. On the planarizing insulating film 7, the storage electrode 11 is disposed such that it is in contact with the source region 6 (or the drain region 6'). Over the entire exposed surface of the resulting structure, a dielectric film 18 and a plate electrode 19 are sequentially formed.
Since the conventional semiconductor memory device has the plane plate type storage electrode, it has an insufficient charge storage capacity when the occupied area of the memory cell thereof is reduced. As a result, the conventional semiconductor memory device is difficult to have a higher integration degree due to the insufficient charge storage capacity.